Details of the proposals for an Edinburgh Airport rail link have been made public.
The cost of the air-rail link plans has been estimated at £500m
At a cost of £500m, the Scottish Executive said the link would open up business and tourism opportunities.
But critics believe the money would be better spent on other rail projects, such as upgrading Edinburgh Waverley Station.
The executive said rail links to both Glasgow and Edinburgh airports were among its top transport priorities.
The cost of the Glasgow rail link is estimated at £140m, but the Edinburgh link is £500m due to tunnelling under the runway to provide a direct link to the rest of the Scottish rail network.
Edinburgh Airport is also due to get a tram service, which is one reason why opponents believe the rail plan is a waste of money.
Mark Ballard, Green MSP for the Lothians, called on ministers to scrap the rail link plan and to invest in the two proposed tram lines for the city, one of which is intended to link the airport with the Haymarket area.
He said: "It is plainly ridiculous that the Scottish Executive should be funding two separate links to the airport which will be in direct competition with each other.
"The railway line will do little to tackle congestion in the area and will bring little benefit to the people of Edinburgh.
"The executive should choose the cheaper alternative which is to build a railway station on the existing line to Fife which runs alongside the airport boundary, and fully fund tram line 2, which will connect Waverley, Haymarket and Edinburgh Park stations, as well as other parts of the city, to the airport."
Transport pressure group TRANSform Scotland said the airport could be served by a new link between existing main lines and the upgrade of Edinburgh's Waverley station is a greater priority.
The company responsible for delivering improvements, Transport Initiatives Edinburgh, said the tram line would serve local passengers while those from further afield would use the main line.
The company's Michael Howell said: "This is a national project which connects the train lines, not just out of Edinburgh, but also to Glasgow and north over the Forth Bridge to Fife and on to Dundee and Aberdeen.
"There is a huge amount of support for this.
"It's the least disruptive option, the most ambitious and the best way to get the cars off the road throughout Scotland and it is a wonderful opportunity for Scotland to move forward."